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| United States Patent |
5,679,186
|
|
Tagashira
, et al.
|
October 21, 1997
|
Pneumatic tire with sipes
Abstract
A pneumatic tire which is improved in uneven tread wear resistance without
sacrificing the on-the-snow/ice running performance. The tread portion
comprises a plurality of blocks, each provided with at least two sipes.
Each sipe extends axially of the tire at an angle of from 90 to 88 degrees
to the circumferential direction of the tire. In a cross section of the
block parallel to the tire equatorial plane, each sipe extends radially
inwardly from the radially outer surface of the block at an angle (.beta.)
of from 2 to 10 degrees with respect to the tire radial direction so that
the radially inner ends of the sipes inclining the same direction towards
the rear surface of the block. The rear surface of the block inclines to
the same direction as the sipes at an angle (.gamma.2) of not more than 30
degrees with respect to the tire radial direction but not less than the
angles (.beta.) of the sipes. The front surface of the block inclines to
the reverse direction to the rear surface.
| Inventors:
|
Tagashira; Kenji (Kobe, JP);
Yamamoto; Akio (Akashi, JP)
|
| Assignee:
|
Sumitomo Rubber Industries, Ltd. (Hyogo-ken, JP)
|
| Appl. No.:
|
568620 |
| Filed:
|
December 7, 1995 |
| Current U.S. Class: |
152/209.23; 152/209.24; 152/902; 152/DIG.3 |
| Intern'l Class: |
B60C 011/12 |
| Field of Search: |
152/209 R,209 D,DIG. 3
|
References Cited
U.S. Patent Documents
| 2109691 | Mar., 1938 | D'Ayguesvives | 152/209.
|
| 4298046 | Nov., 1981 | Herbelleau et al. | 152/209.
|
| 4836257 | Jun., 1989 | Mamada et al. | 152/DIG.
|
| 5022448 | Jun., 1991 | Ochiai | 152/209.
|
| 5044414 | Sep., 1991 | Ushikubo | 152/209.
|
| Foreign Patent Documents |
| 384182 | Aug., 1990 | EP | 152/209.
|
| 157406 | Jul., 1986 | JP | 152/DIG.
|
| 117404 | May., 1990 | JP | 152/209.
|
| 319030 | Dec., 1993 | JP | 152/209.
|
| 727207 | Mar., 1955 | GB | 152/209.
|
| 2093777 | Sep., 1982 | GB | 152/209.
|
Primary Examiner: Maki; Steven D.
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch, LLP.
Claims
We claim:
1. A pneumatic tire comprising a tread portion, said tread portion
comprising a plurality of blocks defined by axial grooves,
each of the blocks having a radially outer surface, a front surface and a
rear surface,
the front surface and the radially outer surface defining a toe edge
therebetween,
the rear surface and the radially outer surface defining a heel edge
therebetween,
the toe edge and heel edge extending axially of the tire,
each of the blocks provided with at least two sipes each extending axially
of the tire, each of said at least two sipes being narrower in width than
each of the axial grooves,
in a cross section of the block parallel to the tire equatorial plane, each
of the at least two sipes extending radially inwardly from the radially
outer surface of the block at an angle .beta. of from 2 to 10 degrees with
respect to the tire radial direction such that radially inner ends of the
sipes incline in the same direction towards the rear surface of the block,
and
the rear surface inclining in the same direction as the sipes at an angle
.gamma.2 of not more than 30 degrees with respect to the tire radial
direction but not less than the angles .beta. of the sipes, and further
the front surface inclining in the opposite direction of the direction of
inclination of the rear surface, wherein
the inclination angle .gamma.1 of the front surface and the inclination
angle .gamma.2 of the rear surface satisfy the following condition:
.gamma.<.gamma. .ltoreq. 30degrees,
the number of the sipes in each block is (n) and the angles of the sipes
are
.beta.1, .beta.2 . . . .beta.n,
in the order from the rear surface to the front surface, and the angles
satisfy the following relationship,
.beta.1>.beta.2>. . . >.beta.n
wherein all of the sipes in each block extend in the same direction with
respect to the tire radial direction.
2. The pneumatic tire according to claim 1, wherein
the depth of the sipes is in the range of from 50 to 70% of the depth of
the axial grooves.
3. The pneumatic tire according to claim 1, wherein
each of the blocks has an axial width in the range of from 12 to 19% of the
width of the tread and a circumferential length in the range of from 16 to
25% of the width of the tread.
4. The pneumatic tire according to claim 1, wherein
the sipes in each of the blocks are arranged such that the block outer
surface is subdivided into substantially equiwide portions.
Description
The present invention relates to a pneumatic tire which is improved in
resistance to tread wear, especially to the heel-and-toe wear caused when
the tire is driven, without sacrificing running performance on the snowy
road.
BACKGROUND OF THE INVENTION
In general, a studless tire for used on the snowy/icy roads is provided
with a plurality of blocks, and each block is provided with axially
extending sipes or slits to increase the coefficient of friction between
the tread surface and the road surface, and thereby to improve the
on-the-snow/ice performance.
As shown in FIG. 4 which shows a sectional view taken in parallel to the
tire equator, of a conventional block (a), the angle .theta. of the sipes
(f) is 90 degrees to the top surface (e) of the block, and the sectional
shape of the block is a trapezoid of which sides (c1) and (c2) facing
axial grooves (b) are the same angle (.gamma.1=.gamma.2) with respect to
the tire radial line (d).
On the other hand, when a tire is driven and/or the tire rotation speed is
higher than the vehicle running speed, the block is subjected to a
shearing force (F) in the opposite direction to the tire rotation
direction, as shown in FIG. 5. As a result, the toe (g) or front edge of
the block in the running direction is liable to lose contact with the road
surface, and the ground pressure of the block (a) is higher in the heel
(h) or rear edge in the running direction than the toe (g). Thus, the
ground pressure distribution is liable to be uneven, and so called heel
and toe wear in which one edge (in this case, heel) wears more quickly
than the other (thus, toe), is also liable to occur. As a result, the
block loses its edge effect quickly, and the running performance
especially on the icy roads is greatly deteriorated.
SUMMARY OF THE INVENTION
It is therefore, an object of the present invention to provide a pneumatic
tire with blocks of which resistance to the heel-and-toe wear which is
caused when the tire is driven is heightened to improve the running
performance on the snowy/icy roads, a result suitable for a driving wheel.
According to one aspect of the present invention, a pneumatic tire
comprises a tread portion comprising a plurality of blocks,
each of the blocks having a radially outer surface, a front surface and a
rear surface,
the front surface and the radially outer surface defining a toe edge
therebetween,
the rear surface and the radially outer surface defining a heel edge
therebetween,
the toe edge and heel edge extending axially of the tire,
each of the blocks provided with at least two sipes each extending axially
of the tire,
in a cross section of the block parallel to the tire equatorial plane,
each of the at least two sipes extending radially inwardly from the
radially outer surface of the block at an angle .beta. of from 2 to 10
degrees with respect to the tire radial direction so that the radially
inner ends of the sipes incline in the same direction towards the rear
surface of the block, and
the rear surface inclining to the same direction as the sipes at an angle
.gamma.2 of not more than 30 degrees with respect to the tire radial
direction but not less than the angles .beta. of the sipes, and further
the front surface inclining to the reverse direction to the rear surface.
Preferably, the inclination angle .gamma.1 of the front surface satisfies a
condition
.gamma.2<.gamma.1.ltoreq.30 degrees.
Given that the angles of the number (n) of sipes in each block are
.beta.1, .beta.2--.beta.n,
in the order from the rear surface to the front surface,
.beta.1>.beta.2>-->.beta.n
is preferable.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention will now be described in detail in
conjunction with the accompanying drawings.
FIG. 1 is a developed plan view of an embodiment of the present invention
showing an example of the tread pattern.
FIG. 2 is a sectional view taken along the line II--II in FIG. 1.
FIG. 3 is a side view of a block showing its deformation when the tire is
driven.
FIG. 4 is a sectional view of the conventional block.
FIG. 5 is a side view of FIG. 4 when the tire is driven.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the pneumatic tire of the present invention comprises a tread
portion 4 which comprises a plurality of, for example three to five, in
this embodiment four circumferential grooves 2 extending continuously in
the tire circumferential direction, and a plurality of axial grooves 3
extending axially of the tire, to divide the tread portion 4 into blocks 9
defining a block type tread pattern.
For the tire inside structure, any known and unknown structure, for example
which comprises a radial ply carcass and a tread reinforcing belt, can be
employed.
Each block 9 has a radially outer surface 5 defining a part of the tread
surface, a pair of side surfaces, and a pair of front and rear surfaces 7
and 6 each facing one of the axial grooves 3. The front surface 7 and rear
surface 6 define a front edge and a rear edge, respectively as the
intersections with the radially outer surface 5. Here, the expression
"front and rear" means that the tire is attached to a vehicle such that
the front edge and rear edge are so disposed in the ground contacting
patch of the tire. Accordingly, when the vehicle runs forward, the rear
edge (heel) contacts with the ground prior to the front edge (toe).
Each block 9 has an axial width BW in the range of from 12 to 19% of the
tread width TW, and a circumferential length BL in the range of from 16 to
25% of the tread width TW.
The axial grooves 3 extend generally straight at an angle of from 90 to 45
degrees, preferably 90 to 70 degrees, more preferably 90 to 88 degrees, in
this embodiment 90 degree with respect to the circumferential direction of
the tire. Thus, the front edge and the rear edge extend generally straight
at the same angle as the axial grooves and substantially parallel with
each other. The blocks 9 in this embodiment are thus substantially a
rectangle at the radially outer surface 5.
Each block 9 is provided in the radially outer surface 5 with at least two
sipes 10. Each sipe 10 is a very narrow groove or cut having substantially
no width, and the width is not more than 1 mm, in this embodiment about
0.5 mm.
The sipes 10 in each block 9 extend generally straight at an angle of from
90 to 45 degrees, preferably 90 to 70 degrees, more preferably 90 to 88
degrees with respect to the circumferential direction of the tire. In this
embodiment, three straight sipes 10 extending across the whole width of
the block at 90 degrees are disposed. Thus, the sipes 10 subdivide the
block outer surface 5 into substantially equiwide portions. Besides a
straight sipe, it is also possible to use a zigzag sipe, for example, such
that only a middle portion is zigzag and the other lateral portion is
straight.
It is preferable that the depth of the sipes 10 is set in the range of from
50 to 70% of the depth of the axial grooves 3 in view of compatibility of
the required block rigidity with the running performance on the snowy/icy
roads.
Therefore, the sipes 10 display the so-called edge effect, that is, the
edges can scratch a slippery road surface, and the apparent coefficient of
friction between the road surface and tire can be increased to improve
running performance on the snowy/icy roads.
As shown in FIG. 2, in the cross section being parallel to the tire
equatorial plane C, each sipe, from its radially outer end at the block
surface 5 to radially inner end 11, inclines at an angle (.beta.1,
.beta.2, .beta.3) in the range of from 2 to 10 degrees, preferably 2 to 4
degrees with respect to a line R drawn in the tire radial direction, such
that the radially inner end 11 inclines to the rear surface 6.
Further, the rear surface 6 is inclined to the same direction as that of
the sipes such that the radially outer edge 13B is located on the front
side of the radially inner edge 13A.
However, the front surface 7 is inclined to the reverse direction to that
of the sipes such that the radially outer edge 13B is located on the rear
side of the radially inner edge 13A.
Therefore, the thickness of a toe-side part 14 defined between the front
surface 7 and the sipe 10 next to the front surface 7 is gradually
increased from the top surface 5 to the base of the block 9, and the
rigidity is increased to decrease the loss of contact of the block surface
in the toe-side part 14 with the road surface during driving. Thus, the
ground pressure distribution of the block surface 5 during driving is more
evened to decrease the heel and toe wear.
Given that the number of the sipes in each block is (n) and the angles of
the sipes are
.beta.1, .beta.2--.beta.n,
in the order from the rear surface 6 to the front surface 7, the angles
satisfy the following conditions,
.beta.1.gtoreq..noteq..beta.2.gtoreq..noteq.--.gtoreq..noteq..beta.n,
and
.beta.1>.beta.n.
The number (n) of the sipes in each block is in the range of from two to
six, usually three or four. By setting the angles in this way, the
rigidity of the block 9 is gradually changed from the rear to front, and
the heel and toe wear can be decreased. Preferably, the angles of the
sipes 10 increases gradually from the front surface 7 to the rear surface
6. That is,
.beta.1>.beta.2>-->.beta.n.
In this case, the block rigidity is increased gradually from the rear to
the front. As a result, the ground pressure distribution can be further
improved to decrease the heel and toe wear.
Further, as shown in FIG. 2, the angle .gamma.2 of the rear surface 6 with
respect to a line R drawn radially from its radially outer edge 13B is not
less than the angle .beta.1 and not more than 30 degrees. That is,
.beta.1.noteq..ltoreq..gamma.2.noteq..ltoreq.30 degrees.
Further, in this embodiment, the angle .gamma.1 of the front surface 7 with
respect to a line R drawn radially from its radially outer edge 13B is
more than the angle .gamma.2 and not more than 30 degrees. That is,
.gamma.2 <.gamma.1.noteq..ltoreq.30 degrees.
Accordingly,
.beta.1.noteq..ltoreq..gamma.2<.gamma.1.noteq..ltoreq.30 degrees.
If the inclination angles (.beta.1, .beta.2, .crclbar.3) of the sipes are
less than 2 degrees, the rigidity of the toe-side part can not be
increased. Contrarily, if the angles are more than 10 degrees, cracks are
liable to occur at the radially inner ends of the sipes.
If the angle .gamma.2 is more than 30 degrees, it is difficult to maintain
the required number of the blocks, that is, the edge effect is decreased.
As a result, on-the-snow running performance is deteriorated. If the angle
.gamma.2 is less than the angle .beta.1, cracks are liable to occur at the
base of the toe-side part 12.
By satisfying the relationship of .gamma.2<.gamma.1.noteq..ltoreq.30
degrees, the rigidity of the toe-side part 14 can be further increased,
and its loss of contact with the ground is effectively prevented to
further improve the resistance to the heel-and-toe wear.
The values used in the above-mentioned limitations are measured under a
standard condition that the tire is mounted on a standard rim and inflated
to a standard inner pressure, but loaded with no tire load.
›Working Example!
Test tires of size 5.60R13 having the block pattern shown in FIG. 1 and the
same construction except for the sipes and angles were prepared and tested
for the following performances. The test results are shown in Table 1.
1) On-the-ice braking performance
A test car provided with test tires was run on a road surface covered with
ice at a speed of 40 km/h and lock braked. Then, the running distance to
stop was measured. In Table 1, the running distance is indicated by an
index based on that the reference tire 1 is 100 . The larger the index,
the better the braking performance.
2) On-the-snow braking performance
The test car provided with test tires was run on a road surface covered
with snow at a speed of 40 km/h and lock braked. Then, the running
distance to stop was measured. In Table 1, the running distance is
indicated by an index based on that the reference tire 1 is 100. The
larger the index, the better the braking performance.
3) Heel and toe wear resistance
The test tires were mounted on the front wheels of a 1800 cc front wheel
drive car, and the test car was run for 4,000 km on asphalt paved
highways. Then, the difference between the wear amount in the heel and
that in the toe was measured. In Table 1, the difference is indicated by
an index based on that the reference tire 1 is 100. The larger the index,
the better the resistance to heel-and-toe wear.
It was confirmed through the tests that the tires according to the present
invention were improved in the heel-and-toe wear resistance while
maintaining the on-the-snow/ice braking performance. Further, it is also
confirmed that such effects can be obtained regardless of the tire size.
As described above, in the pneumatic tires according to the present
invention, uneven wear which deteriorates the road grip can be decreased
without sacrificing the on-the-snow/ice running performance.
TABLE 1
__________________________________________________________________________
Ref. 1
Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ref. 2
Ex. 5
Ex. 6
Ex. 7
Ex. 8
Ex. 9
Ex. 10
__________________________________________________________________________
Angle (deg.)
.beta.1 0 2 3 4 10 3 3 3 3 3 4 4
.beta.2 0 2 3 4 10 3 3 3 3 3 3 4
.beta.3 0 2 3 4 10 3 3 3 3 3 2 2
.gamma.1 20 20 20 20 20 20 20 30 15 10 20 20
.gamma.2 10 10 10 10 10 0 3 20 15 20 10 10
Test results
On-the-ice braking
100 100
100
100
100
100 100
100
100
100
100
100
On-the-snow braking
100 100
100
100
100
101 101
98 100
100
100
100
Heel & Toe wear
100 103
105
107
107
95 102
108
103
102
108
106
__________________________________________________________________________
The invention being thus described, it will be obvious that the same may be
varied in many ways. Such variations are not to be regarded as a departure
from the spirit and scope of the invention, and all such modifications as
would be obvious to one skilled in the an are intended to be included
within the scope of the following claims.
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